In the oil and gas industry, stimulation with an acid is performed on a well to increase or restore production. In many situations various sizes of casing are placed in a well to prevent water table supply contamination, provide isolation between various formations to limit drilling fluid losses, contain high pressure formations, provide a means to secure down hole production equipment such as electric submersible pumps, pressure sensing equipment and isolation production strings etc. To secure these various lengths of casing cement is utilized which typically is of a very high density and resistant to degradation by produced well fluids as well as conventional acids, such as hydrochloric acid. After the well is drilled, a completion program is typically commenced which will stimulate the formations or zones of interest to stimulate oil and gas fluids to flow from the formation into the wellbore. During these stimulations fluids, gels, proppants, chemicals and gases such as nitrogen will be pumped into the formation via the casing perforations (or other completion technique).
One of the challenges facing the industry is breaking down, or cleaning the residual cement and debris left in the perforations or breaking through the actual cement sheath in certain completion techniques such as cemented sleeve ports. During a cemented sleeve port completion operation, coiled tubing tools (or a shifting ball) will be deployed capable of “sliding open” the sleeve which is placed and cemented in position during the casing placement stage of the wells drilling cycle (at the end of the drilling cycle). Once these sleeves are opened there is typically a cement sheath inhibiting flow from the casing to the formation. Acids are typically deployed prior to the frac fluid stage (this acid stage is called a “spearhead”). Most cement blends commonly utilized in the oil and gas industry have minimal acid solubility, hindering the effectiveness of most conventional acids.
Another major challenge operators face is executing remedial (cement) work on existing wells for either the purpose of sealing a leak in the cement portion of the well (causing a communication of well fluids to an undesirable section of the formation or well face), or for an abandonment of a well whose life cycle has expired. In both of these examples there is usually a need to seal any leaks that may be present by executing a “cement squeeze”. Typically an acid is pumped prior to the new cement to be placed to ensure an unobstructed pathway for the placement of the new cement to seal the leak or communication. In these situations it is sometimes difficult to obtain an acceptable injection rate of the cement due to the inability of current acids typically used in the industry to solubilize the cement sufficiently.
Common day to day operations utilizing organic and mineral acids in the oil and gas industry include three major types of acid applications: matrix acidizing, fracture acidizing, and spearhead breakdown acidizing. A matrix acid treatment is performed when acid is pumped into the well and into the pores of the reservoir formation below the fracture pressure. In this form of acidization, the acids dissolve the sediments and mud solids that are inhibiting the permeability of the rock, enlarging the natural pores of the reservoir (wormholing) and stimulating flow of hydrocarbons. While matrix acidizing is done at a low enough pressure to keep from fracturing the reservoir rock, fracture acidizing involves pumping highly pressurized acid into the well, physically fracturing the reservoir rock and etching the permeability inhibitive sediments. This type of acid treatment forms channels or fractures through which the hydrocarbons can flow.
There are many different mineral and organic acids used to perform an acid treatment on wells. The most common type of mineral acid employed on wells to stimulate production is hydrochloric acid (HCl), which is useful in stimulating carbonate reservoirs.
One of the major challenges faced in the oil and gas industry from using hydrochloric acid is the extremely high levels of corrosion (which is countered by the addition of ‘filming’ corrosion inhibitors that are typically themselves toxic and harmful to humans, the environment and equipment, and are very difficult to maintain in solution with the acid over a period of time); reactions between acids and various types of metals can vary greatly but certain metals, such as aluminum and magnesium, are very susceptible to major effects causing immediate damage. Also, hydrochloric acid produces hydrogen chloride gas which is toxic (potentially fatal) and corrosive to skin, eyes and metals. At levels above 50 ppm (parts per million), it can be Immediately Dangerous to Life and Health (IDHL). At levels from 1300-2000 ppm death can occur in 2-3 minutes. The current invention involves an acid that is non-fuming, eliminating this risk for industry personnel.
The inherent environmental effects (organic sterility, poisoning of wildlife etc.) of hydrochloric acids in the event of an unintended or accidental release on surface or downhole into water aquifers or other sources of water are devastating which can cause significant pH reduction of such and can substantially increase the toxicity and could potentially cause a mass culling of aquatic species and potential poisoning of humans or livestock and wildlife exposed to/or drinking the water. An unintended release at surface can also cause a hydrogen chloride gas cloud to be released, potentially endangering human and animal health. This is a common event at large storage sites when tanks split or leak. Typically if near the public, large areas need to be evacuated post event. Because of its acidic nature, hydrogen chloride gas is also corrosive, particularly in the presence of moisture.
The inability for conventional acids and blends of such to biodegrade naturally without neutralizing the soil results in expensive cleanup-reclamation costs for the operator should an unintended release occur. Moreover, the toxic fumes produced by mineral and many organic acids (acetic and formic in particular) are harmful to humans/animals and are highly corrosive and/or explosive potentially. Transportation and storage requirements for these acids are quite restrictive and taxing in such that you must typically haul the products in specialized acid tankers or intermediate bulk containers (IBC) that are rated to handle such corrosive products, bringing exposure dangers for personnel exposed to handling.
Another concern is the potential for spills on locations due to the high corrosion levels of conventional acids which can cause storage container failures and/or deployment equipment failures i.e. coiled tubing or fracturing iron failures caused from high corrosion rates (pitting, cracks, pinholes and major failures). Other concerns include: downhole equipment corrosion causing the operator to have to execute a work-over and replace down hole pumps, tubing, cables, packers etc.; high levels of corrosion on surface pumping equipment resulting in expensive repair and maintenance levels for operators and service companies; the requirement of specialized equipment that is purpose built to pump acids greatly increasing the capital expenditures of operators and service companies; and the inability to source a blended product locally or very near its end use.
Another problem for industry utilizing conventional acids, and certain acid replacements is high temperature stability. Several operations in the oil industry expose fluids and equipment to very high temperatures (some upward of 200° C.). The compositions used in these various operations need to withstand these high temperatures without losing their effectiveness. These compositions must be capable of being used in operations over a wide range of temperatures while not affecting the equipment with which it comes in contact and yet still remain stable. The current invention has stability up over 180 degrees Celsius and will not lose its solubilizing characteristics as temperature increases as many mineral acids do. Having a high temperature, chemically stable, acid is very attractive to industry for multiple functions such as, but not limited to, acid fracturing, remedial operations, freeing stuck drilling pipe, spearhead acids, high temperature scale mitigation, and constant injection applications for SAGD (Steam Assisted Gravity Drainage) programs.
When used to treat scaling issues on surface due to water/fluid precipitation, acids are exposed to personnel and mechanical devices as well as expensive pumping equipment causing increased risk for the operator and corrosion effects that damage equipment and create hazardous fumes. Conventional acids typically need to be blended with fresh water (due to their intolerance of highly saline water, causing precipitation of minerals) to the desired concentration requiring companies to pre-blend off-site as opposed to blending on-site with produced water thereby increasing costs associated with transportation.
When using an acid to pickle tubing or pipe, very careful attention must be paid to the process due to high levels of corrosion, as temperatures increase, the typical additives used to control corrosion levels in acid systems begin to degrade very quickly (due to the inhibitors “plating out” on the steel) causing the acids to become very corrosive and resulting in damage to equipment/wells. Having to deal with ‘live’ acid during the back flush process is also very expensive as conventional acids typically are still at a very low pH and toxic. It is advantageous to have an acid blend that can be exported to production facilities through pipelines that once spent or applied, is commonly a neutral pH greatly reducing disposal costs/fees.
Typically, up to 10 chemical additives can be required to control various aspects of the acids performance adding to obstacles in the handling and shipping logistics. Having an alternative that only requires minimal additives is very advantageous.
In wells that have a high degree of sour gas (hydrogen sulphide) and carbon dioxide, in its composition, there is always a high concern of corrosion. Pipelines are especially of concern, as many variables can create unwanted corrosion and pitting attack on the steels. Any presence of water containing hydrogen sulphide in combination with a certain amount of chlorides will create an acidic effect on the steel, potentially creating corrosion related failures. Any amount of protective scaling mechanism that is generated on the sour gas pipeline walls can also be subject to scale disruption in the presence of chlorides, exposing the surface to corrosion attack. The use of a hydrochloric acid in these types of applications is obviously not possible, due to the high level of chlorides in the mineral acid. Utilizing a high strength acid for downhole scale removal that has virtually no chloride level is an obvious advantage to the application.
Acids perform many actions in the oil and gas industry and are considered necessary to achieve the desired production of various petroleum wells, maintain their respective systems and aid in certain functions (i.e. remedial well intervention, or abandonment of a well that has expired its life cycle). The associated dangers that come with using acids are expansive and tasking to mitigate through controls, whether they are chemically or mechanically engineered. Eliminating, or even simply reducing, the negative effects of acids while maintaining their usefulness is a struggle for the industry, especially at higher temperatures encountered downhole. As the public demand for the use of cleaner/safer/greener products increases, companies are looking for alternatives that perform the required function without all, or most of the, drawbacks associated with the use of conventional acids.
The composition according to the present invention can ideally be used in various oilfield operations; spearhead acid, fracking operations, injection/disposal well injectivity treatments, scale treatments (surface and subsurface-wells equipment, pipelines, facilities), filter cake removal, tubing pickling, bullhead/annular squeezes and soaks, cement squeezes, fluids pH control, stuck pipe treatment.
Therefore, the present invention answers the need for both a simpler manufacturing process and abridged, novel organic acid compositions for use in high volume operations in oilfields throughout the world.
Consequently, there is still a need for compositions for use in the oil industry which can be used over a range of applications which can decrease a number of the associated dangers/issues typically associated with acid applications to the extent that these acid compositions are considered much safer for handling on worksites, stable at a range of temperatures, and which are chloride-free.